This invention relates generally to calculators and improvements therein and more particularly to programmable calculators that may be controlled both manually from the keyboard input unit and automatically by a stored program loaded into the calculator from the keyboard input unit or an external magnetic record member.
Computational problems may be solved manually, with the aid of a calculator (a dedicated computational keyboard-driven machine that may be either programmable or nonprogrammable) or a general purpose computer. Manual solution of computational problems is often very slow, so slow in many cases as to be an impractical, expensive, and ineffective use of the human resource, particularly when there are other alternatives for solution of the computational problems.
Nonprogrammable calculators may be employed to solve many relatively simple computational problems more efficiently than they could be solved by manual methods. However, the keyboard operations or language employed by these calculators is typically trivial in structure, thereby requiring many keyboard operations to solve more general arithmetic problems. Programmable calculators may be employed to solve many additional computational problems at rates hundreds of times faster than manual methods. However, the keyboard language employed by these calculators is also typically relatively simple in structure, thereby again requiring many keyboard operations to solve more general arithmetic problems.
Many programmable calculators constructed according to the prior art have employed step oriented memories and have handled memory transfer of conditional or unconditional transfer statements through the use of absolute step references. This technique leaves the user with sole responsibility for statement address modification in the event a transfer statement is edited, thus increasing the user's workload, as well as the chances for introduction of errors, during program editing operations. In addition, these prior art calculators rarely include language features useful in performing iterative looping functions encountered in programming complex problems.
These earlier step oriented calculators produced printed program listings that were very difficult to read because information syntactically representing a single statement was generated by several separate key actuations and then listed in a similar fashion with the information associated with each key being listed on a separate line.
Conventional programmable calculators are limited as to the complexity of the problems they are able to solve because of memory capacity limitations. Magnetic tape storage has been employed in some calculators to store program segments and data for use during execution of a program, thereby effectively increasing the size of the calculater read-write memory. These magnetic tape storage systems have been of limited usefulness, however, because of the relatively long access times involved.
Conventional programmable calculators in the low cost range have presented a communication problem for the user in that they typically have not employed output printers with fully formatted alphanumeric printing capabilities. It would be advantageous in calculators of this type to provide a low cost thermal printer, for example, that may be called upon by the user to print a variety of characters and numeric data according to a format designated by the user.
Conventional programmable calculators have been arranged to respond to power turn on by entering a standby mode, after which the user may enter a program from the keyboard or from a magnetic tape cassette, for example, for execution by the calculator. This arrangement is disadvantageous in that it requires of the user a considerable degree of knowledge regarding operation of the calculator. It would be advantageous to provide a programmable calculator that automatically responds to application of operating power by loading a program from an external magnetic record member into the calculator memory and by subsequently automatically initiating execution of that program.